We all know that working for a company with a toxic culture is unpleasant and stressful. But research on the impacts of toxic workplaces is still surprisingly grim. 

One study found a toxic workplace triples your risk of depression. Research out of Harvard shows that firing a toxic jerk adds more than twice as much to a company's bottom line as hiring a superstar. Another recent study showed a toxic workplace was the single biggest predictor of whether employees would join the Great Resignation and head for the door. 

All of which should make it crystal clear that you don't want to lead (or work for) a company with a toxic culture. But that begs a simple but important question. What exactly makes a culture toxic? 

We all have vague ideas about what kind of behavior qualifies as toxic, but recently a team out of MIT set out to find a more scientific answer to this question. (They are the same group of researchers behind the study I mentioned above about toxic culture being a predictor of resignations.) 

To figure out exactly what causes a problematic workplace to rise to the level of true toxicity, the team combed through 1.3 million Glassdoor reviews, using text analysis to determine what sort of words and topics in reviews led to the biggest reductions in a company's culture score. Here are the five biggest signs of toxicity they uncovered

1. Incivility and disrespect 

Your mom always told you to say "please" and "thank you." Turns out, she was right--basic manners really are a big deal. Companies where employees complained their colleagues lacked civility or showed no concern for the dignity of others had a culture rating .66 lower on a five-point scale. Comments about lack of respect were even more predictive of a poor Glassdoor culture score than if employees used extreme language like "dumpster fire" or "soul-crushing" in reviews. 

2. Non-inclusive environment 

Being less welcoming to certain groups doesn't just cost a company the talent of those who are left out because of discrimination. It also seriously lowers the morale of those who do join. 

A failure to fully include the LGBTQ community lowered companies' average rating exactly as much as a general lack of civility, while inequity directed at those with disabilities lowered it .59 and against racial minorities .58. A range of other types of unfairness showed slightly smaller but still significant effects, from age discrimination (scores slid .44) to gender inequality (.40) to nepotism (.40). 

"Collectively, this cluster of topics is the most powerful predictor of whether employees view their organization's culture as toxic," write the researchers. So, maybe sit up and pay a little better attention next time someone offers you advice on creating a more inclusive environment

3. Unethical behavior 

When you cut ethical corners, employees notice and they really don't like it. Unethical behavior at a firm lowered its Glassdoor rating by .62. Failure to comply with regulations nudged it down .44. Reviewers used words like "shady," "cheat," "deceive," "mislead," "make false promises," and "smoke and mirrors" when describing companies they deemed unethical. 

4. Cutthroat competition

It can be tempting for managers to tolerate unpleasant behavior in pursuit of higher performance, but this research suggests you're likely to face stiff penalties in terms of employee dissatisfaction and eventually resignations in the longer term. Backstabbing behavior and ruthless competition at a company lowered its score .61 on average. 

The researchers are careful to note that what they mean here isn't run-of-the-mill turf disputes or moaning about uncooperative colleagues. Instead they're referring to companies where reviewers used phrases like "dog-eat-dog" and "Darwinian" to describe the culture or "talked about co-workers who 'throw one another under the bus,' 'stab each other in the back,' or 'sabotage one another.'"

5. Bullying

It's no shock that employees aren't keen on being bullied or seeing their colleagues being bullied. Companies that tolerated bullying, harassment, and other forms of open hostility saw their Glassdoor scores take a big hit. The most common problem behaviors in this category include yelling, demeaning others, verbal abuse, or talking down to others. 

Thankfully, full-on bullying of this type is relatively rare, but it is hugely impactful on the culture. "In their review, but just 0.8 percent described their manager as abusive," the authors write. "When employees did mention abusive managers, however, it depressed their culture rating by an additional 0.50 on average."

Outright bullying might not be common, but the researchers caution that toxic cultures are far from rare. "You might think that toxic culture is somebody else's problem, limited to a handful of high-profile flameouts like Wells Fargo or the Weinstein Company and not something your organization needs to worry about. Unfortunately, cultural toxicity is widespread," they write. 

So, armed with this list, take a hard look at your own company's culture and make absolutely certain you don't see any of these five hallmarks of a truly toxic culture.